In recent years, from the viewpoint of environmental protection, a hybrid electric vehicle with small CO2 emissions and an electric vehicle that does not emit CO2 (hereinafter collectively referred to as an electrically powered vehicle) have come into widespread use. A battery pack is mounted on this electrically powered vehicle as an energy supply source that supplies energy to a driving motor and other electric systems.
The battery pack is provided with a plurality of cell modules and a packaging case housing the plurality of cell modules.
Each of the cell modules is such that a plurality of electric cells are electrically connected as one package. That is, each of the cell modules is an assembled battery formed of a plurality of electric cells.
The packaging case is provided with a tray on which cell modules are arranged and a cover that covers the cell modules on the tray. For example, the tray includes a bottom portion on which a plurality of cell modules are arranged in a matrix shape in planar view (in a condition in which a plurality of cell modules are arrayed lengthwise and crosswise in planar view), a lower circumferential wall portion which rises from the outer circumference of the bottom portion, and a lower flange portion which extends outward from the upper end of the lower circumferential wall portion. The cover includes a top portion having a shape corresponding to an open portion of the tray, an upper circumferential wall portion which suspends from the outer circumference of the top portion, and an upper flange portion which extends outward from the lower end of the upper circumferential wall portion.
And the cover covers the open portion of the tray including the plurality of cell modules arranged on the bottom portion, bolts are inserted to the lower flange portion and the upper flange portion that abut each other, nuts are screwed to the bolts, and the tray and the cover are fastened. As a result of this, the lower flange portion of the tray and the upper flange portion of the cover come into surface contact with each other, and the internal space of the packaging case for housing the cell modules becomes liquid-tight.
This battery pack is mounted to a bottom portion of an electrically powered vehicle. That is, because the weight and size of the whole battery pack mounted on an electrically powered vehicle becomes very large due to the necessity of securing electrical capacity, from the viewpoints of driving stability, arrangement of other components and the like, this battery pack is arranged in the bottom portion of an electrically powered vehicle (cf., Patent Document 1, for example).
Incidentally, as described above, since the battery pack mounted on the electrically powered vehicle is arranged on the bottom portion of the vehicle, moisture or water easily attaches to the outer surface of the packaging case due to car washing or splashing of water during driving. For this reason, the liquid-tightness between the tray and the cover (between the lower flange portion and the upper flange portion) needs to be sufficiently secured. However, in the conventional battery pack, the lower flange portion and the upper flange portion are caused to come into surface contact with each other to make the internal space of the packaging case liquid-tight. For this reason, when the pressure of the liquid on the packaging case is high, moisture or water may enter the internal space of the packaging case from between the lower flange portion and the upper flange portion.
For example, a high-pressure washer that ejects water or a liquid detergent (hereinafter, referred to as wash fluid) is used in some cases for car washing or maintenance. When high-pressure wash fluid is sprayed to the underbody of the electrically powered vehicle or the bottom of the car body, the wash fluid may enter the internal space of the packaging case from between the lower flange portion and the upper flange portion, and the wash fluid may cause short circuits and the like to damage the entire cell modules or the electric cells.
In addition to the above problem, the conventional battery pack also has a problem that attachment and detachment work of the cover associated with the inspection or replacement of the cell modules or the electric cells is troublesome. That is, bolts and nuts are used to fasten the tray and the cover in the conventional battery pack. The nuts need to be supplied to a plurality of portions (a plurality of fastening positions set around the tray and the cover) to fasten the tray and the cover, and the nuts arranged on the plurality of portions need to be recovered to remove the cover from the tray. Therefore, the conventional battery pack has a problem that very troublesome work needs to be performed when the cover is attached or detached in association with the inspection or replacement of the cell modules and the like.